The present invention relates to reflectors or transflectors useful in, for example, reflective type or transflective type liquid crystal display devices.
Transflective type liquid crystal display devices used in highly information-oriented portable terminals or the like have functions of both transmissive type liquid crystal display devices using a backlight and reflective type liquid crystal display devices. For example, they can be used as a reflective type liquid crystal display device without backlighting in bright settings and as a transmissive type liquid crystal display device with backlighting in the dark, so that they can save power consumption as compared with transmissive type liquid crystal display devices. Transflective type liquid crystal display devices are equipped with a transflector on the rear of a liquid crystal cell having the same polarizer as used in transmissive type displays, for example. Such a transflector may be formed by vapor-depositing a metal such as silver or aluminium to such an extent to permit the transmission of light on a film surface which has been roughened by, for example, xe2x80x9csand mat methodxe2x80x9d comprising bombarding a polyester film with hard particles to roughen the film, xe2x80x9ccoating mat methodxe2x80x9d comprising coating a polyester film with a resin fluid containing particles to roughen the film, xe2x80x9cparticles-adding mat methodxe2x80x9d comprising charging a polyester film with a large amount of organic particles to roughen the film, or xe2x80x9cblend mat methodxe2x80x9d comprising blending a polyester film with a heterogeneous polymer to roughen the film. Liquid crystal display devices using such a transflector can be used as both reflective type and transmissive type liquid crystal display devices because the transflector can serve as not only a reflector but also a diffuser with backlighting as a result of the metal deposition on the roughened film to such an extent to permit the transmission of light. Thus, such a transflector diffuses both reflected light and transmitted light, so that, when used as a reflector, it can prevent a visibility by observers from decreasing by excluding direct reflections on the reflector (the term xe2x80x9cdirect reflectionxe2x80x9d used herein means such an unwanted image formed on the reflector or transflector by the reflection of external light as in case of a mirror) and/or widening a viewing angle and also make the reflected light whiter to provide display images being easier to see, and, when used as a diffuser, it can homogeneously diffuse the backlight to provide display images being easier to see.
On the other hand, reflective type liquid crystal display devices have attracted attention, because they make it possible to reduce their weight and power consumption as compared with transmissive type or transflective type liquid crystal display devices using backlighting. Reflective type liquid crystal display devices are equipped with a reflector on the rear of a liquid crystal cell having the same polarizer as used in transmissive type displays, for example. Such a reflector may be obtained by vapor-depositing a metal on a film having been roughened in the same manner as used for the transflector described above and increases diffused reflection by surface roughening, so that, when used in reflective type liquid crystal display devices, it can prevent a visibility by observers from decreasing by excluding direct reflections on the reflector and/or widening a viewing angle and also make the reflected light whiter to provide display images being easier to see.
However, a problem associated with using such a reflector or transflector has been that their surface roughness directly influences the quality of display images and therefore using a reflector or transflector having such a rougher surface lowers the quality of display images to make it difficult to display clearly defined images. Further, a surface having less roughness decreases the diffused reflections. Therefore, a problem associated with using such a surface with less roughness has been that increased direct reflections formed on the reflector or transflector and a narrowed viewing angle make a visibility by observers decreased and that insufficient whiteness of the reflected light decreases a quality of display image.
As a result of careful studies to solve the above problems, we accomplished the present invention on the basis of the novel finding that without surface roughening process, good reflection characteristics can be obtained by using a reflector or transflector having a light-scattering layer and a light reflective or transflective layer, wherein the light-scattering layer comprises a resin layer containing fine particles dispersed therein, the ten-point average roughness xe2x80x9cRzxe2x80x9d on the surface of said light-scattering layer is less than 2 xcexcm, the refractive index ratio of said fine particles to the resin layer excluding said fine particles is from 1.001:1 to 1.2:1 and said light-scattering layer has a thickness of 3-50 xcexcm, and that the quality of display images can be remarkably improved when such a reflector or transflector is used in image display devices such as reflective type or transflective type liquid crystal display devices.
Accordingly, the present invention relates to:
(1) a reflector or transflector having a light-scattering layer and a light reflective or transflective layer wherein the light-scattering layer comprises a resin layer containing fine particles dispersed therein, the ten-point average roughness xe2x80x9cRzxe2x80x9d on the surface of said light-scattering layer is less than 2 xcexcm, the refractive index ratio of said fine particles to the resin layer excluding said fine particles is from 1.001:1 to 1.2:1, and said light-scattering layer has a thickness of 3-50 xcexcm;
(2) a reflector or transflector as defined in the above item (1) wherein the refractive index of the resin layer excluding said fine particles is 1.3-1.55;
(3) a reflector or transflector as defined in the above item (1) or (2) wherein the amount of said fine particles is 5-50 parts by weight per 100 parts by weight of the resin layer excluding said fine particles;
(4) a reflector or transflector as defined in any one of the above items (1) to (3) wherein said fine particles have an average particle size of 0.5-30 xcexcm;
(5) a reflector or transflector as defined in any one of the above items (1) to (4) wherein said fine particles are in the form of true spheres;
(6) a reflector or transflector as defined in any one of the above items (1) to (5) wherein said light reflective layer is a film having a metal-deposited surface;
(7) a reflector or transflector as defined in the above item (6) wherein said metal-deposited surface is a surface deposited with silver or aluminium;
(8) a reflector or transflector as defined in any one of the above items (1) to (7) wherein said light-scattering layer is adjacent to said metal-deposited surface;
(9) an optical film having a reflector or transflector as defined in any one of the above items (1) to (8); and
(10) an image display device comprising a reflector or transflector as defined in any one of the above items (1) to (8).